1. Field of the Invention
The subject matter of this invention concerns improvements in laminates comprised of polymer foam core sandwiched between facing sheets, and a method of producing such laminates which enhances their physical and thermal properties.
2. Description of the Prior Art
It is well known to produce laminate products on a continuous conveyor processing line, wherein the laminates have a polymer foam core flanked by opposed facing sheets adhered to the upper and under surface of the core. Many arrangements are used commercially for this but generally involve advancing a bottom sheet, which may be of flexible material such as paper, plastic film, metal foil, sheet metal and the like, along a conveyor surface while depositing on that sheet a reactive liquid polymer mix. The mix foams as it ages during further progress with the sheet along the conveyor, gradually rising into a blanket covering the entire facing sheet. An upper facing sheet is also applied after laydown of the foam mix, to complete the laminate, both upper and lower sheets becoming bonded to the foam as this continues to develope during advance along the conveyor, thus providing a finished product such as wallboard having a foam core sandwiched between facing sheets.
Examples of this general procedure are illustrated in prior patents of which Carlson et al Nos. 3,215,581, Edwards 3,453,168, Wooler 3,702,274, Kolakowski et al 3,837,771, Anderson et al 3,933,548, Forrester 4,019,938, Hipchen et al 4,028,158 and Tippmann 4,149,840, are the most pertinent to this invention known to the inventors herein. The objective of the prior patents in each case is to obtain continuous production of panelboard having various types of facing sheets bonded to an expanded polymeric form core, wherein the surfaces of the finished panelboard are smooth, planar, the finished board is of uniform thickness and the foam core is well adhered to the facing sheets and is of uniform density. Achieving this desired result presents very real practical problems in large scale continuous production, since many variables such as changes in foam mix formulation, ambient temperature conditions, as well as programmed altering of physical dimensions (e.g., thickness) of the panelboard are commonly involved. Maximizing the physical properties of the product, while coping with the numerous variables mentioned above, requires considerable skill on the part of personnel controlling the process and uniformity is not always achieved even by highly skilled personnel. Improvements in the process which assist an operator in getting consistently uniform product are accordingly of considerable commercial importance.